1. Field of Invention
The present invention relates to a torque wrench and, more particularly, to a device for calibrating a torque wrench.
2. Related Prior Art
A mechanical device for calibrating a torque wrench is disclosed in Taiwanese Patent Publication No. 538859. The mechanical device includes a shell 10, an axle 21, a block 23, an elastic bar 24, a positioning element 25 and a meter 40. The axle 21 includes a middle section inserted in the shell 10 and two ends 22 located out of the shell 10. The block 23 is attached to the middle section of the axle 21. The elastic bar 24 includes an upper end inserted in the axle 21 and a lower end in contact with the positioning element 25 located in and attached to the shell 10. The meter 40 includes a probe 42, an indicator 43 and a scale (not numbered). The probe 42 includes a lower end in contact with the block 23 and an upper end connected to the indicator 43. The indicator 43 is rotatable with respect to the scale. In operation, a boxed or open end 51 of a torque wrench 50 is engaged with one of the ends 22 of the axle 21 while the shell 10 is secured to a workbench or held by a user. The axle 21 is rotated by the torque wrench 50. The block 23 is rotated while the elastic bar 24 is deformed. The probe 42 is lifted so that the indicator 43 is rotated relative to the scale. Thus, the torque exerted on the axle 21 is measured by the calibrating device. However, the reading of the torque is affected by the angle of the observation of the indicator 43 relative to the scale. Moreover, there are errors in such a mechanical configuration so that the reading of the torque might not reflect the real value of the torque exerted on the axle 21 by the torque wrench 50.
An electric device for calibrating a torque wrench is disclosed in Taiwanese Patent I341235. The electric device includes a shell 20, a rod 30, an elastic bar 40, a sensor 60 and an electric display unit 70. The rod 30 includes a middle section (not numbered) inserted in the shell 20 and two ends 34 located out of the shell 20. The elastic bar 40 includes an end inserted in the axle 21 and another end in contact with a rotating element 54 attached to a frame 52 located in and attached to the shell 20. The sensor 60 is a strain gauge attached to the elastic bar 40. The electric display unit 70 includes a display 72 electrically connected to the sensor 60. In operation, a boxed or open end of a torque wrench is engaged with one of the ends 34 of the rod 30 while the shell 20 is secured to a workbench or held by a user. One of the ends 34 of the rod 30 is rotated by the torque wrench via the rod 30, which is accordingly rotated. Thus, the elastic bar 40 is deformed. The sensor 60 senses the deformation of the elastic bar 40 and accordingly sends a signal to the electric display unit 70 which accordingly calculates the value of the torque exerted in the rod 30 and shows the value on the display 72. The pivoting of the torque wrench is however not smooth.
Therefore, the present invention is intended to obviate or at least alleviate the problems encountered in prior art.